Vacuum tube construction



May 10, 1932. w. L. KRAHL VACUUM TUBE CONSTRUCTION Filed March 11. 1927numlum inunnoh INVENTOR W447i? [0M5 69/4/14 ,1 ATTORNEY Patented May 10,1932' UNITED STATES PATENT OFFICE WALTER LOUIS KRAHL, OF MONTOLAIR, NEWJ, ASSIGN'OR TO ARGTURUS RADIO TUBE COMPANY, OF HARRISON, NEW JERSEY, ACORPORATION OF DELAWARE vacuum roian consrancrron Application filedMarch 11, 1927. Serial No. 174,511.

This invention relates to a thermionic device and to a methodofoperating the same for the amplification, detection, rectification andthe like, of alternating or fluctuating currents, and more particularly,to a method and apparatus for energizing the cathode of a thermionicvacuum tube by means of alternating or fluctuating current in suchmanner that the output is independent of fluctuations of the energizingcurrent.

It is an object of this invention to provide a thermionic relay orthermionic vacuum tube which may be energized by alternating orfluctuating currents without the production of'noise or hum incidentalto the use of such alternating or fluctuating currents.

It is a further object of this invention to provide a tube having afilamentary cathode and connections associated therewith, and

2 circuits adapted to function therewith, such that the potentialbetween the grid and filament and the potential between the filament andplate is substantially independent of changes or fluctuations infilament heating 2:! current.

It is still another object of this invention to provide such a devicehaving terminals thereon so positioned and arranged that the device maybe inserted in a standard socket, and also having an additional terminaland internal'connections whereby the device may be utilized in existingapparatus.

It is still a further object of my invention to provide a method ofoperating a thermionic relay by energizing the filament of such relay bymeans of alternating or fluctuating currents while impressing thevarious control voltages in such manner that undesired voltages orvoltage changes do not appear in the output circuit.

Still other objects of my invention'will be apparent from thespecification.

The features of novelty which I believe to be characteristic of myinvention are set forth with particularity in the appended claims. Myinvention itself, however, both as to its fundamental principles and asto its practical applications, will best be understood by reference tothe specification and accompanying drawings, in which according to myinvention, showing the con- 5 nections between the internal elements ofthe tube and the terminals; and

Fig. 3 is a similar view of a modified form thereof.

In accordance with my invention, I provide among others, certain of theelements usually found in thermionic relays, for example: an evacuatedenvelo e having therein an anode, a control electrode and a cathode, thecontrol electrode preferably being in the form of a grid surrounding thecathode, and lt)hrtahanode in the form of a plate surrounding Inaccordance with my invention, I utilize a special form of filamentarycathode consistlng of a pair of branches orlegs, and connections uponthe base of the device in such a manner that alternating or fluctuatingcurrents are supplied to the'filamentary cathode and flow through thetwo legs or branches in series, whereas the control volta e applied" 7between the grid and filamentan the voltage applied between the filamentand plate are impressed between the respective electrodes and the commonpoint of the two filament branches.

It will be understood that if the input and output circuits areconnected to the filamentary cathode at a common point, the potentialbetween the anode and cathode and that between the input electrode andcathode will not be appreciably affected by the voltage drop in thecathode. It will also be seen that if this common point of contact ofoutput and input circuits in the filament is the mid-point, it will beat the mean alternating current potential of the filament. It is alsoobvious that if a. filament having suflicient thermal capacity beutilized, the thermionic emission of said filament will not varyappreciably with current pulsations when heated with alternating orfluctuating currents of the frequencies normally utilized forhouse-lighting.

It will be understood that disturbances due to electrostatic andelectromagnetic fields aris- 10o ing from an alternating or fluctuatingsource of heatin current, wil vary with the power consumptlon of thefilament. It is' therefore desirable to utilize oxides which emit at low5 Itemperatures, so that a low-resistance filament may be operated withthe least current. Oxides of aluminum have been found particularlyeffective atlow operating temperatures, but oxides-of barium, strontium,and others known to the art may also be utilized. Copper or nickel maybe used advantageously as a resistance material, but other metals, suchas platinum, tungsten, molybdenum and thorium might also be used.

Referring now more particularly to Fig. 1, I have illustrated anembodiment'of my inyention as applied in a thermionic tube comprising anevacuated container or envelope 10, having a base 11 secured to one endvthereof. The base 11 is preferably in the form of a cylindrical shell12 of conducting material, having an end plate 13 of insulating materialwhich is provided with axially extending terminals v14, 15, 16 and 17pro- I j'ectin therefrom. Within the tube envelope there is provided asingle stem or press 18, through which are passed all of the leads andsupports for the various elements of the tube.

In the particular arrangement shown, there is provided an anode 19 oftubular formation and approximately circular cross-section comprisingplane portions 20, laterally ex-' tended and bent on themselves to formsupporting tubes 21, adapted to-receive the sup- 8 parting rods 22mounted on the press 18.

ithin the anode 19, there may be positioned a control electrodeor grid23 in the form of a helical coil of wire 24 mounted on support rods 25extending into press 18. Within the space defined by grid 23, there maybe placed cathode 26. w 7

It will be noted that the cathode 26 is a cylindrical rod or wire, andthe ends 29 and 30 are connected to conducting support rods 31 and 32embedded in the press. A conductor 33 is provided, connected toconductor 34 which in turn, is connected to the mid point 35 of thefilament.- It will therefore e seen that all of the electrodes aresupported and the leads thereto passed through the single press 18. 1

Within the stem of the tube, the base connections are 'made from thetube elements as follows: from anode 19 through support 22 5 and lead 36to terminal 14; from control electrode 23 through support 25 and lead 37to terminal 16 from the mid point of the filament through conductor 34,conductor 33, to

the metallic shell 12 of the base 11. The ends of the filament, 29 and30, are connected through leads 40 and 41 respectively to terminals 17and 15 In addition, the envelope or container may be coated with a layerof conducting material such as metal in the form of foil glued thereonor applied by de osition, which coat ing may be connected t rough themetallic shell 12 to a suitable source of potential, ei-

ther ground or a point positive or negative with respect thereto.

Referring now to Fig. 2, it will be seen that the filament may beenergized by connecting a suitable source to the terminals 15 and 17.Any suitable source may be utilized, for example: a-commerci'alalternating current power outlet of ap roximately volts, thecurrent-from who may be assed through the primary 45 of a suitab etransformer having a secondary 46, the terminals of which are connectedto terminals 15 and 17.

It will now be seen that a signal voltage may be applied between thegrid or control electrode and the cathode which will be substantiallyindependent of the cathode.

alternating current potential providing that this signal potential beimpressed between the grld and the cathode mid-point: and similarly, aplate voltage may be applied to the tube, which is independent of theheating current if applied between the anode and the cathode mid-point,which permits the use of the tube as an amplifier, detector, rectifier,or the like, utilizing commercial alternating current as a source offilament supply.

If it is desired to utilize tubes of a construction herein described inconnection with a standard radio receiving circuit without alteration ofthe internal wiring of said receiver, additional external terminals,such as described in co-pending application Serial No. 140,245, filedOctober 8th, 1926, and diagrammatically illustrated in" Fig. 3 of thepresent case by references 70 and 71 may be used. Connections from theinternal elements of the tube may be made as illustrated in Fig. 3.

While I have shown and described certain preferred embodiments of myinvention, it will be understood that modifications and changes may bemade as will be understood by those skilled in the art without departingfrom the spirit and scope of my invention as covered by the appendedclaims.

I desire to claim as my invention:

1. A thermionic relay comprising an evacuated container having thereinan anode; a control electrode; and a filamentary cathode adapted to beheated by fluctuating currents to cause electron emissioma base securedto said container; four terminals positioned on tween the mid-point ofsaid cathode and said fifth terminal; a connection between the surfacefilm and the fifth terminal; and connections between opposite ends ofsaid cath- Odeand the remaining two base terminals.

2. A thermionic relay comprising an evacuated container having thereinan anode, a control electrode and a filamentary cathode adapted to beheated by fluctuating currents to cause electron emission; a basesecured to said container; said base having a conducting shell; fourterminals positioned in said base according to standard practice, saidbase shell forming a fifth terminal; a metallic film on said container;a connection between said anode and one of said terminals; a connectionbetween said control electrode and another of said terminals; aconnection between the mid-point of said cathode and the base shell; aconnection between the container film and base shell; and a connectionbetween opposite ends of said cathode and the remaining two baseterminals.

In testimony whereof, I aflix my signature.

.WALTER L. KRAHL.

